In pursuit of higher engine efficiencies, higher turbine inlet temperatures have been relied upon to boost overall engine performance. This can result in gas path temperatures that may exceed melting points of turbine component constituent materials. To address this issue, dedicated cooling air is extracted from a compressor section and is used to cool the gas path components in the turbine, such as rotating blades and stator vanes for example, incurring significant cycle penalties.
One method of controlling cooling flow involves the use of metering plates. Metering plates are positioned in a flow path between an upstream channel and a downstream channel. A meter plate is typically a single piece of thin sheet-metal with at least one hole that has a size that is significantly smaller than the downstream channel. These types of plates are effective in metering flow; however, the plates deflect flow in a way that can degrade downstream flow attachment.
For example, a jet stream exiting a hole in the meter plate can induce a region of poor attachment, i.e. a dead zone, when the downstream channel has a direction of flow that is not aligned with the direction of flow of the jet stream. This dead zone can lead to higher overall pressure losses and degradation in heat transfer on the non-flow attached wall. This adversely affects cooling efficiencies.